The present invention relates to an ink jet printer, and specifically to an ink jet printer usable as a hard copy apparatus in which an image data from a computer is recorded by a jet of ink.
Conventionally, in a printer in which recording is conducted by binary gradation data, ON/OFF recording is conducted corresponding to binary data.
For example, in an ink jet printer, image data for each one-jetting of each nozzle of a print head having a plurality of jet nozzles is transferred to a driving IC of the head for each time, and ink-jetting is conducted by transferred image data and an image is formed.
FIG. 11 is an illustration showing a drive signal waveform supplied to a head and conditions of jetting a drop of liquid in a jet nozzle, as a model. As shown in FIG. 11, the following processes are repeated by the drive signal waveform, in which a jetting nozzle composed of a piezo-element, or the like, is expanded (1.fwdarw.2), then, contracted (3) and jets a drop of liquid of ink, and returns again to an initial condition (4).
Recently, gradation recording is conducted in various types of printers, and conducted also in an ink jet printer in the same manner as other printers.
As a gradation recording method, there is a method in which the number of dots jetted for a pixel is changed. According to this method, by changing the number of dots to be jetted, the same effect can be obtained as that obtained when dimensions of a dot at jetting are changed.
Incidentally, there is sometimes a case where a sufficient jetting can not be conducted when viscosity of ink is changed by the temperature change. In this case, ink jetting can not be accurately conducted, resulting in a decrease of image quality.
Generally, viscosity is increased two times every time when temperature decreases by 10.degree. C. Therefore, when an ink jet printer is used in the low temperature environment such as early in the morning in winter, sufficient ink jetting can not be carried out for a period of time after the start of the printer.
Further, even if the ink jet printer is warmed up after its start, the temperature of ink of unused color is not increased, thereby, sufficient ink jetting can not be carried out.
Further, the head is in an air-cooled condition by the movement of the head, the temperature of the unused color ink tends to be lowered. Further, even in the used color ink, the overall head is in the water-cooled condition when the cooled ink passes through the nozzle, and therefore, the temperature is hardly increased.
Due to such the problems, a proposal is made in Japanese Patent Publication Open to Public Inspection No. 133062/1984, in which the ink is heated by providing a heater near the head of the ink jet printer.
However, when the heater is provided as described above, there are following problems:
(1) the number of parts is increased near the head, and the structure becomes complicated; PA0 (2) it is difficult to widely control heating of the ink in a liquid accommodation chamber in the head; PA0 (3) efficiency is low when the heating of the ink in a liquid accommodation chamber in the head is widely controlled; PA0 (4) power consumption due to a heater resistance body is large.
Further, in the ink jet printer having heads for a plurality of colors for color image formation, a problem also occurs in which color balance is lost if the temperature of each head is not almost the same. Further, it is extremely difficult to maintain the head temperature of each color uniform even when the heating control by the above-described heater is applied.